Commercial Gas-to-Liquid (GTL) systems for converting natural gas to in to hydrocarbon liquid transportation fuels are often based on a multiplicity of complex refinery-based operations using oxygen-blown conversion of natural gas (or other fossil fuel-based resources) into synthesis gas (a.k.a. syngas) containing hydrogen (H2) and carbon monoxide (CO). The syngas is converted into liquid hydrocarbon fuels and waxes through a series of Fischer-Tropsch Synthesis (FTS) reactions that are catalytically activated by a transition-metal based catalyst. The main FTS reaction is the conversion of hydrogen and carbon monoxide into the liquid hydrocarbon fuel and water:nCO+2nH2—{CH2}—+nH2O  [Reaction 1]
As Reaction 1 shows, each molecule of CO requires two molecules of H2 to produce hydrocarbon products (liquid fuels and waxes) and one molecule of water (H2O). In Biomass to Liquid (BTL) systems, the gasification of biomass to produce a hydrogen-deficient syngas (containing an approximately 1:1 mole ratio of CO:H2) cannot sustain Reaction 1. Thus, for BTL systems, the CO:H2 ratio may be adjusted through the Water-Gas-Shift (WGS) reaction to convert a portion of the water vapor and CO in the gasified biomass to additional H2 with CO2 as a byproduct:CO+H2OH2+CO2  [Reaction 2]
In many BTL systems, the WGS reaction is catalyzed by an iron-based Fischer-Tropsch catalyst so that approximately one-half the CO in the gas reacts with an equal molar amount of water vapor (which may be sourced from the Reaction 1) to produce H2 and CO. The remaining CO is converted to FTS products.
In most large-scale GTL and BTL systems, highly-polished syngas (containing only CO and H2) is converted to heavy paraffinic FTS waxes at pressure of 250 to 400 psig. In a series of refinery-based operations, the FTS wax products are cracked and hydrogenated into gasoline and diesel-fuel products. These GTL facilities are usually very large (typically producing several thousands of barrels per day of diesel product) and demand on-site oxygen and hydrogen generation plants to support the gasification and fuel upgrading systems.
Unfortunately, large-scale GTL and BTL systems require significant investments of capital to build. They also need to receive the proper approvals from regulatory, environmental, and zoning authorities that can limit the ability to build these systems near the biomass sources they will utilize to make the FT fuels. The systems also need to be coupled to or located near fuel transportation infrastructure to deliver the FT fuels to their final destination (e.g., gas stations). Given the large investment of capital and difficult source to end use logistics that are typical for these large scale systems, there is a need for new methods and systems to generate FT fuels.